Growth of vaccinia and variola viruses in the one-day-old fertile hen's egg.

The cultivation of viruses in fertile hen's eggs has been widely utilized, providing many advantages for virological studies, since the pioneering work of Woodruff and Goodpasture (1931). In most of such works, however, eggs more than 5 days old have been used. Recently, Yoshino (1956) described a technique for experimental infection of the 1-day-old egg, revealing that such an early embryo supported growth of herpes simplex virus as sufficiently as did the 13-day-old embryo's chorioallantois. His results attracted special interest of the author in light of the data provided by Needham (quoted in Baldwin, 1950) which demonstrated that nitrogen was excreted in the form of ammonium in the very early stage of embryonic development of the hen's egg while it took the forms of urea and ureic acid successively in later stages. The different modes of nitrogen excretion may suggest the presence of different metabolic pathways between the early and later stages. Nevertheless, the above-cited experiments revealed the high susceptibility of the 1-day egg to herpes virus. Hence, our concern has been focussed on the questions of (1) whether 1-day eggs are susceptible to other viruses than herpes virus, too, (2) whether there can be a virus to which 1-day eggs are more susceptible than older eggs, (3) whether there can be a virus which is not readily grown in older eggs but which can be easily propagated in 1-day eggs, and (4) whether viral progeny yielded in 1-day eggs, if any at all, shows any difference from parent virus in viral properties. To go in details in these problems, it was first desired to collect various data along this line. The present work has been carried out with such considerations in mind, employing vaccinia and variola viruses, and specially designed to detect any possible variation of these viruses following infection of the 1-day egg.